Manufacturing environments typically include large machines with a number of moving parts, such as factory robots, welding machines and the like, which can pose a safety risk to factory workers who work in close proximity to robotic devices. An assessment of the level of risk of harm to operators at a machine or process entails the collection of qualitative and quantitative data with regard to potentially hazardous situations.
International standard ISO 14121—“Safety of machinery—Principles for risk assessment”—defines that “risk” comprises two factors namely: consequences (or severity of injury) resulting from a hazardous situation; and probability of occurrence of the hazardous situation. The probability of occurrence itself is divided into two constituent parts namely: frequency and duration of exposure to a hazard; and lack of possibility of avoidance of harm. Such factors can be generically applied to all types of machinery for estimating the level of risk.
Consequently, a risk assessment is routinely performed to determine various risk factors that might be encountered from the machines. Such assessment includes determining the types of risk, e.g. the paths of moving parts, force of impact, high temperatures, and the degrees of risk associated with each type. In order to maximize the effectiveness of the risk assessment and risk estimation it is essential that accurate and detailed data is available upon which judgments concerning the basic factors above can be made.
Risk assessments are used to implement risk reduction measures, and to reduce risk to acceptable levels. In particular, safety related control systems are commonly integrated into machinery to reduce risk. In the case of a robotic device with swinging arms, a security perimeter is established to define a safe area. The security perimeter can be a fence with an entry gate having an interlock switch that shuts down the device upon entry. The perimeter can also be established by floor markings, alone or in combination with a photoelectric array for disabling the device if the plane of the perimeter is broken by the operator.
In general, the standard approach to risk assessment is satisfactory if all the factors can be anticipated. Very often they are embedded in the usage and training documentation supplied with the machine. But at all these stages, it is typical that some aspects are not yet known and some decisions have to be based on assumptions about future machine usage characteristics. If the actual machine usage characteristics differ from those assumed it may cause the risk assessment to become invalid.
Such unanticipated variations in the risk factors can arise due to various internal and external conditions. It may happen that a robotic device may operate under load-bearing conditions outside of specified parameters. Also, unpredictable machine behavior may result in the event of a power failure or control system failure. Additional risk may be encountered when multiple persons are present within a designated work area, or when there exists variations in operator skill. Also, various factors may change over time, due to machine wear and seasonal or climatic variations in temperature and humidity.
Despite all the aforementioned variations, it is not uncommon for a manufacturing operation to still be working with an original risk assessment that is no longer valid. This can result in unanticipated hazards to machine operators, leading to worker injuries and unexpected machine servicing, accompanied by production line delays. Such failures defeat the purpose of the initial risk assessment.
The type of safety related control system is specified according to the risk assessment. If the machine usage characteristics are such that the risk assessment becomes invalid, it could mean that the safety-related control system does not provide the type of functionality or level of integrity that is then actually required.
Typical reasons for variations in machine usage characteristics from the original risk assessment include, e.g. increased frequency or duration of machine operation, higher power levels, improper maintenance, processing of unexpected materials, unexpected environmental conditions, use by persons with competency levels lower than expected, occurrence of mechanical and software-related system faults, non-standard system components or operational modifications.
Risk assessment is ideally an iterative process that should be conducted at all phases of a machine's design, manufacture, commissioning and operation, with the results being handed on from one stage to the next, so as to take into account variations in risk factors. However, since risk assessments are typically performed manually during installation or maintenance of the machine components, it is prohibitively labor-intensive process to conduct ongoing manual risk assessments of all machines in a factory setting.
Therefore, there is a need to overcome the aforementioned exemplary deficiencies associated with conventional systems and devices.